Anastrozole (Arimidex)

• About anastrozole
• Common side effects
• Occasional side effects
• Important points to remember

Anastrozole is also called Arimidex. It is a type of hormone therapy called an aromatase inhibitor, and is used to treat breast cancer.

Many breast cancers are stimulated to grow by the female sex hormones oestrogen and progesterone. These breast cancers are called ‘hormone sensitive’ or ‘hormone receptor positive’ and can be treated with drugs that block the effects of these hormones. Although it is not understood why, some oestrogen receptor negative breast cancers can also be controlled by anastrozole.

Although women past their menopause don’t produce oestrogen from their ovaries, they still produce a small amount by turning other sex hormones (androgens) into oestrogen. Androgens are made by your adrenal glands, these are the small glands above your kidneys. Androgens need an enzyme called aromatase to turn them into oestrogen. This change happens mainly in fatty tissue, muscle and the skin. Aromatase inhibitors stop or ‘inhibit’ aromatase, so it can’t change the androgen into oestrogen.

These drugs are only suitable for women who've had their menopause. But some trials are looking into whether combining aromatase inhibitors with a drug called Zoladex can help some premenopausal women with breast cancer.

You take anastrozole as a tablet, once a day.

We've listed the side effects associated with anastrozole below. You can use the links to find out more about each side effect. Where there is no link, please use the search box at the top of the page. Or look at our general information about hormone therapies section in the cancer treatment section.

Many women will have one or more of the following side effects

• Menopausal symptoms including hot flushes and sweats in more than 1 out of 10 (10%) women, and decreased interest in sex (reduced libido)
• Painful joints - this happens in about 1 out of 10 (10%) women treated
• Tiredness or fatigue - this happens in about 1 in 10 (10%) of women treated
• Skin rashes - these are usually mild. You should let your doctor know if you have a rash. This happens in about 1 in 10 women (10%)
• Feeling or being sick - happens in about 1 in 10 women (10%) treated. It is usually mild and can be easily controlled by anti sickness medication.
• Headaches
• Painful hands with weakened grip and numbness and tingling - carpal tunnel syndrome

• Mood changes
• Cough and breathlessness - this affects less than 1 in 10 (10%) women
• Loss of bone density - this is caused by a lack of oestrogen over a long period of time. When your bones are less ‘dense’ they may break more easily. You should have a 'DEXA scan' to check your bone density before you start treatment.
• Loss of appetite
• Increased level of cholesterol in the blood. This is usually only slightly raised and you will have regular blood tests to check this
• Hair thinning
• Diarrhoea - drink plenty of fluid and tell your doctor if diarrhoea becomes severe, or continues for more than 3 days
• Dryness of the vagina
• Vaginal bleeding. This mainly happens when women have changed from one type of hormone therapy to another during the first few weeks of treatment. You should tell your doctor or nurse if the bleeding continues. This affects fewer than1 in 20 (5%) of women treated.

The side effects above may be mild or more severe. A side effect may get better or worse through your course of treatment, or more side effects may develop as the course goes on. This depends on

• How many times you've had the drug before
• Your general health
• The amount of the drug you have (the dose)
• Other drugs you are having

Some side effects are inconvenient or upsetting but not damaging to your health.

Some side effects are serious medical conditions and need treating. Where we have urged you to contact your doctor, this is because

• Your side effect may need treating
• Your drug dose may need reducing to try to prevent the side effect

Tell your doctor about any other medicines you are taking, including vitamins, herbal supplements and other over the counter remedies - some drugs can react together.

Talk to your doctor, pharmacist or nurse about all your side effects so that they can help you manage them. You should have a contact number for your chemotherapy nurse, clinic or ward nurse. You can ring if you have any questions or problems. They can give you advice or reassure you. If in doubt, call them.